1. Field of the Invention
The present invention relates to a semiconductor light emitting device including a semiconductor light emitting element such as an LED (light emitting diode), and a vehicle lamp comprising the semiconductor light emitting device.
2. Description of the Related Art
There have been known semiconductor light emitting devices which have a semiconductor light emitting element (hereinafter also called simply a light emitting element) that emits light having a specific wavelength when a current is injected and a fluorescent substance that absorbs part of light from the light emitting element to emit light having a wavelength longer than that of the light from the light emitting element in combination. With these semiconductor light emitting devices, light from the light emitting element and light from the fluorescent substance are mixed, so that mixed light of a desired emission color can be obtained.
For example, Patent Literature 1 describes a semiconductor light emitting device which comprises a case having a cavity formed therein, an LED element provided at the bottom of the case, and resin containing a fluorescent substance and filled in the cavity to bury the LED element. Patent Literature 2 and Patent Literature 3 describe a semiconductor light emitting device wherein the top and side surfaces of a semiconductor light emitting element are covered with a wavelength converting layer having a fluorescent substance dispersed therein. In this configuration, by making the coating thickness of the wavelength converting layer uniform which covers the semiconductor light emitting element, the proportion of light wavelength-converted by the wavelength converting layer becomes uniform across the entire area, so that the mixing ratio of blue light emitted from the semiconductor light emitting element to yellow light emitted from the fluorescent substance becomes uniform, and thus mixed light with less color unevenness can be obtained. For example, in the case where a semiconductor light emitting device is configured with a blue light emitting element having an emission wavelength of about 450 nm and a YAG-based yellow fluorescent substance having an emission wavelength of about 570 nm in combination, mixed light with a degree of chromaticity on the line segment joining point B and point Y on a chromaticity coordinate system shown in FIG. 1 can be obtained. For example, when trying to obtain mixed light with a degree of chromaticity corresponding to point W on line segment B-Y, the coating amount (thickness) of the wavelength converting layer should be adjusted as needed according to the brightness of the light emitting element.
For example, a light emitting element made of group III nitride-based semiconductors is produced by crystal growing sequentially an n-type semiconductor layer, a light emitting layer, and a p-type semiconductor layer, which are made mainly of a group III nitride-based semiconductor, over a sapphire substrate. An n-electrode is formed on the surface of the n-type semiconductor layer exposed by partially removing the p-type semiconductor layer and the light emitting layer from the p-type semiconductor layer side as described in, e.g., Patent Literature 4 and Patent Literature 5. Or, as described in Patent Literature 6, the n-electrode may be formed on the surface of the n-type semiconductor layer exposed by removing the sapphire substrate after a support substrate is bonded to the surface of the p-type semiconductor layer. Sometimes the former is called a lateral element and the latter is called a vertical element because of the placement relationship between the n-electrode and the p-electrode. For each electrode of the light emitting element, in addition to a bonding pad, line portions extending over the surface of the semiconductor film may be provided in order to promote current diffusion in the semiconductor film. By providing the line portions, the entire light emitting layer can be made to function effectively, thus improving light output and luminous efficiency.